The present invention relates to a semiconductor device, and in particular to a semiconductor technology which is effectively applicable to packages of a large scale integrated circuit having a high packaging density.
Semiconductor chips have heretofore been molded to seal with a resin for protecting the same. Various methods are used for positioning and mounting the leads on the semiconductor chip prior to molding.
For example, a leadframe having a tab at a center thereof is used. In the prior art, a method of connecting electrode pads positioned in the vicinity of the periphery of a chip with corresponding inner leads by bonding wires has been known.
A common problem in prior art semiconductor packages resides in that cracks are formed along a parting line of a mold which is an exit of lead wires of a metal leadframe.
Another problem resides in that a path of invasion of environmental pollutant along the metal leads into the semiconductor chip from outside is relatively short.
A further problem resides in that bonding wires should not cross each other since bonding wires necessary to connect the inner leads with electrode pads of the semiconductor chip are relatively long and input/output terminals are alternately assigned thereto.
In order to overcome the above problems, a resin molded semiconductor device including a plurality of inner leads are bonded to the active area of the semiconductor chip with an insulating film interposed therebetween, in which the inner leads are electrically connected with the semiconductor chip through bonding wires, common inner leads (bus bar inner leads) are provided in the vicinity of a longitudinal central line of the active area of the semiconductor chip was proposed in JP-A-61-241959, laid open Oct. 28, 1986, which corresponds to U.S. Ser. No. 724,736 filed Apr. 18, 1985.
U.S. Ser. No. 07/373,742, filed Jun. 30, 1989 and assigned to Texas Instruments Inc., discloses a leadframe having a pair of elongated conductive buses and first and second groups of conductive leads arranged on opposite sides of the power buses, in which the areas of the conductive leads are substantially identical with each other, thereby providing a balanced capacitance.
Proceedings of the 1988 IEEE Electronic Components Conference, pp. 552-557 reports an area wire bond plastic structure in which a leadframe has lead strips extending into the center of the package in the form of leads and busbars. The leadframe is laminated directly to the surface of a chip.
Conventionally, a leadframe of the type having busbars (common leads) at its central portion includes support leads provided on an outer frame of the leadframe separately from leads serving as terminals for a semiconductor device on a semiconductor chip. This is for the purpose of supporting the semiconductor chip when the leadframe, having been properly positioned on the chip and molded, is subjected to cutting and shaping operations.
However, there is a difficulty that since heat dissipation may be insufficient at an area of the semiconductor chip where heat generation is high, this deteriorates the reliability of the semiconductor device.